1. Field of the Invention
The present invention relates to an organic electroluminescent apparatus, and more particularly to an organic luminescent material of the organic electroluminescent apparatus.
2. Description of Related Art
An electroluminescent device is a semiconductor device capable of converting electric energy into photonic energy with high conversion efficiency. Common applications of the electroluminescent device are an indicator light, a display panel, a luminescent device of an optical read/write head, and the like. The electroluminescent device has characteristics such as getting rid of a viewing angle problem, an easy process, low cost, a high response speed, a wide application temperature range and being full-color, therefore meeting requirements of display characteristics in a multimedia time and having a prospect of becoming a mainstream of a next-generation flat-panel display.
Generally, an organic electroluminescent apparatus includes an anode, an organic luminescent layer and a cathode. The organic luminescent layer includes a host luminescent material and a guest luminescent material. Holes and electrons in the organic electroluminescent device are mainly delivered into the host luminescent material for recombination, thereby producing energy, and the energy is transferred into the guest luminescent material to produce light. Therefore, the host luminescent material needs to have a desirable electron and hole transport property, and a triplet energy level of the host luminescent material should be greater than or equal to that of the guest luminescent material, to avoid energy loss caused by energy return.
Therefore, if the triplet energy level of the host luminescent material needs to be improved, a length of a conjugated chain in a molecule of the host luminescent material should be shortened. However, if the length of the conjugated chain in the molecule of the host luminescent material is shortened, a molecular weight of the molecule is reduced, and the reduced molecular weight of the host luminescent material decreases thermal stability (a glass transition temperature is used as a pointer in the following) of the host luminescent material.